Method of using resin powders to cure solvent-free inks

ABSTRACT

The disclosure is concerned with a method of curing solvent-free inks by application of a powdered resin to a freshly printed surface. Powder, which does not adhere to the ink, is removed and the printed surface then is passed through a heating tunnel where the resin melts, thereby curing the ink. Optionally, the printed surface may be leveled mechanically following curing. Such leveling produces a higher gloss. Air pollution which normally is caused by solvent fumes in conventional processes is eliminated by this method. Moreover, heat energy is conserved as the need to vaporize a solvent and to carry-off the heated vapors is eliminated.

United States Patent 1 Neuberg William B. Neuberg, Garden City, NY.

[75] Inventor:

[73] Assignee: Shamrock Chemicals Corporation, New York, NY,

122] Filed: Mar. 19, 1974 [21] Appl, No.: 452,512

[52] US. Cl ,1 427/27; 101/426 [51] Int. Cl 341m 1/00; B051) 5/02 [581Field of Search 117/13, 17, 29, 46 FC, 117/15, 19, 25; 101/426 [56]References Cited UNITED STATES PATENTS 1,084,742 11/1914 Jacobs et a1.117/13 2,110,219 3/1938 Creen et a1 101/420 2,317,372 4/1943 Gessler eta1. 101/426 2528,1150 11/1950 Thorp et a1 r 101/426 2,681,473 6/1954Carlson 117/17.5 3,083,116 3/1963 Berndt.,. 117/13 3,440,076 4/1969Vuurio 117/13 3,444,809 5/1969 Ohkubo et a1. r. 117/25 1 1 Oct.7, 19753,464,353 9/1969 Bach et a1 101/470 3,523,031 8/1970 Walters 117/293,617,328 11/1971 Newman 4 117/29 3,640,749 2/1972 Lorenz 117/175Primary ExaminerMichael Sofocleous Attorney, Agent, or Firm Brumbaugh,Graves, Donohue & Raymond [57] ABSTRACT The disclosure is concerned witha method of curing solvent-free inks by application of a powdered resinto a freshly printed surface. Powder, which does not adhere to the ink,is removed and the printed surface then is passed through a heatingtunnel where the resin melts, thereby curing the ink.

Optionally, the printed surface may be leveled mechanically followingcuring, Such leveling produces a higher gloss.

Air pollution which normally is caused by solvent fumes in conventionalprocesses is eliminated by this method. Moreover, heat energy isconserved as the need to vaporize a solvent and to carry-off the heatedvapors is eliminated,

11 Claims, 1 Drawing Figure METHOD OF USING RESIN POWDERS TO CURESOLVENT-FREE INKS BACKGROUND OF THE INVENTION It is known that powderedresins can be used in the drying of printing inks. Among these areanti-offset powders which coat the entire printed surface and therebyprovide spacing between adjacent printed sheets (US. Pat. No.2,110,219).

Another use of resin powders is in thermographic printing processes. Aresin powder, having a particle size in the 30 to 200 mesh range, isapplied to the ink on the freshly printed surface and melted to create araised effect which simulates engraving. The particle size of the powdercontrols the thickness or degree of raise of the printing. Thisthickness is generally between 0.1 and 0.2 mm. 100 and 200 microns) andit is necessary that the particle size of the powder be controlled to aclose degree of uniformity. The particle size is limited by the size oftype used in printing since particles, which are too big, will overflowthe sides of the letters and cause the edges to be uneven. Particles,which are too small, will not produce a proper degree of raise, and willalso produce an area of mottled appearance on areas of heavy inkcoverage. Thermographic inks may or may not contain solvent.

Another printing process, described in US. Pat. No. 2,3 17,372 utilizesa finer resin powder, having an average particle size of about 16 to 60microns, to coat the freshly printed ink. This process does not create araised effect in contrast to the thermographie process. However, the inkin this process must contain a solvent to solubilize the resin powder.The presence of solvent has two major drawbacks. Firstly, sufficientheat to vaporize the solvent must be provided and the heated vapors thenmust be removed from the heating area; this results in a waste of heatenergy. Secondly, air pollution is caused by the expelled solventvapors.

Methods of printing with solvent-free ink also are known. However, pastmethods of printing with nonpolluting solvent-free inks have severaldisadvantages (John W. Vanderhoff De-inking the lnk Industries Position"American lnk Maker, April, 1973, pp. 42-46). Such inks require severalhours to dry by oxidation and have been overcoated with a thin,fastdrying, transparent coating that protects the ink film until itdries. These coatings often are alcoholic soluble propionate resinswhich are permeable to oxygen. Thus, there is solvent effluent from thecoating resin solution which creates air pollution.

DESCRIPTION OF THE INVENTION It has now been discovered thatsolvent-free inks can be rapidly and economically cured with powderedresins. Thus, in accordance with the present invention, a solvent-freeink is conventionally applied to a surface. Powdered resin in which 95%of the particles have a size between about 1 and 26 microns and anaverage particle size of between about 5 and microns is then applied tothe surface and it adheres to the wet ink. Subsequently, any excesspowder is removed. The printed surface is passed through a heatingtunnel where the resin is melted. At this stage, the melted resincombines with the liquid ink. This combination cures when cooled toambient temperature ifa thermoplastic resin is used or cures bypolymerization if a thermosetting resin is used thus creating anon-raised, printed surface with a thickness below about 7 microns e.g.,about 0.5 to 5 microns.

It is critical in the present invention to utilize a solvent-free ink.As defined herein, solvent-free inks fall into the following categories,among others:

I. Drying Oil Vehicle Inks: These inks are formulated and manufacturedfrom linseed, tung, soya, safflower, dehydrated castor, poppyseed andoiticia oils and may be modified with drying catalysts, such as metalsoap dryers.

2. Drying Oil Alkyds: These inks are made from the above-defined dryingoil vehicle inks by additions of glycerine and isophthalie acid insufficient amounts to achieve a desired working viscosity for the inks.

3. Resin Modified Drying Oils and Drying Oil Alkyds: These inks are madefrom phenolic or maleic resin modified drying oils or drying oil alkyds.

4. Gum Rosin and Tall Oil Rosin: These inks are made from eitherunreacted gum rosin or tall oil rosins.

5. Non-Drying Oils: Inks made from mineral oils or petroleum oils, forexample, newspaper inks.

6. Epoxy, Polyurethane and Polyamide Modified Inks: Although some ofthese inks may contain solvents, inks of this type without solvents maybe used. Selection of the ink is at the discretion of the printer whomust decide which ink is best for a particular surface. If the surfaceis paper, the printer may chose one ink; if the surface is metal, he maychose another ink.

The resin that is used in the process of the present invention must beground to a particle size finer than about 325 mesh. The optimumparticle size is between about 1 and 26 microns. However, it is criticalto have an average particle size between about 5 and 10 microns. Thesepowders may be produced by grinding, cryogenic grinding, air milling,air classifying, spray drying, crystallization, or by combinations ofthese processes or procedures. A typical powder has the followingparticle size count as measured micro- Average particle size equals thesum of nd divided by the sum ofn, i.e., 2612/485 to 4068/485 or 5.38 to8.38 microns.

Any suitable resin may be employed in this invention provided that itcan be powdered to the aforementioned required particle size, melted atthe appropriate temperature, fused to a compatible composition with theink and solidified on cooling to form a tack-free, immobile surface.This, therefore, includes both thermoplastic and thermosetting resins aswell as resins which become thermosetting when combined with the ink oradditives used in the ink. The following resins,

among others, are suitable: rosin, rosin modified with maleic. fumaric,phenolic or inorganic components rosin, petroleum, polyamide, natural,alkyd, epoxy, acrylic, urethane, amino, wax-modified, pigmentorfiller-modified, plasticizer-modified and inorganics.

Wax may be added optionally to the powdered resin in an amount rangingfrom about /2 to 3'7? by weight in order to increase rub resistance. Itis necessary, however, that the wax have a particle size comparable tothat of the powdered resin. The following waxes, among others, may beused: paraffin, microcrystalline, natural, synthetic, compounded,polyethylene, and polytetrafluoroethylene. Similarly, other materialsmay be used as additives, including colorants, cure promoters, levelingagents, and functional additives among others.

The powdered resin must be applied to the freshly printed surface by amethod which will give a relatively uniform coating. The quantity ofpowdered resin used is usually kept to the minimum required to cure theink. The preferred method of powdered resin application is byelectrostatic powder coating. Thus, in one embodiment of the presentinvention, electrostatic guns are used to release a precisely controlledpowder distribution by means of controlling an electrostatic charge onthe resin particles and an opposite charge on the freshly printedsurface.

The electrostatic guns are housed in a chamber having entry and exitopenings to permit passage of the freshly printed surface therethrough.This chamber confines the powder to the area of application so that thepowder will not pollute the air.

In other embodiments, the powder may be applied with an air gun. Afluidized bed also may be used wherein the freshly printed surface ispassed through an atmosphere containing the powder, or an electrodynamicdevice may be employed.

Powder, which does not adhere to the ink, may be removed prior tocuring. in a preferred embodiment, an air knife is used for thispurpose. An air knife is an apparatus having a slit or a series of holesthrough which air is forced. Suitable air pressures are in the range ofbetween about and 50 pounds per square inch. The air stream is directedagainst the powder coated surface and blows the powder off the areaswhich are not printed with ink. The air used for this purpose may beionized to promote dissipation of the electrostatic charges. Thisapparatus may be housed in its own chamber or in the same chamber as theelectrostatic guns and downstream of the area where the powder isapplied. It is preferable to recycle the powder which is removed.

Curing proceeds by heating in a tunnel to effect a surface temperatureabout 50 to l50F above the melting point of the resin. Direct flame orinfrared heating tunnels among others may be used for this curing step.

The printing process being continuous and dynamic by its nature requiresthe adjustment of inking rate, fountain solution, and other variables toarrive at the desired product on the delivery end of the press.Likewise, the rate of powder application as controlled by thepositioning of the powder guns, choice of voltages, feed rates, andother controls must be adjusted to be compatible with the press.Generally. it is desired to use only that amount of powder which isrequired to cure the ink. This will vary from one printing applicationto the next depending on the amount of coverage, the stock, and thequality of work desired.

When the powder application rate is cut back for greatest economy, thereresults a slight reduction in gloss. Further reduction of powder resultsin incomplete curing; therefore, the powder must be then increased.Taking a proof signature at this stage of adjustment reveals anirregular surface when viewed under magnification. Using a low powermicroscope, it can be seen that resin particles tend to have fused withthe individual dots in the printing halftone structure.

It has been found that increased gloss can be achieved by leveling thesurface mechanically prior to allowing it to cool or in the process ofcooling. This can be accomplished by means of the chill rolls normallyemployed to complete the curing of heat-set printing or it can be doneby means of additional rolls. There must be sufficient pressure or dragto level the resin coating, but not so much as to smear the printing.The resulting surface has a glassy appearance when viewed under a lowpower microscope. The thickness is reduced to a range of less than onemicron. Furthermore, still lower rates of powder application can now beutilized and still maintain complete curing.

Thus, in accordance with this invention. it is now possible to cure aconventionally applied solvent-free printing ink rapidly, in a highspeed process, without producing raised print. The problem of airpollution caused by heated solvent vapors or the solvent containingprotective overcoatings utilized in prior art pro cesses is eliminatedby the present invention. Moreover, as compared with prior art processesthat utilize heat to dry the ink, energy is conserved by the presentinvention as it is not necessary to provide heated air to carry offsolvent vapors.

DESCRIPTION OF THE DRAWING A typical apparatus for carrying out thepresent invention is illustrated in the attached schematic drawing. Aroll 1 of paper continuously feeds paper 2 to a conventional printingpress 3 where the solvent-free ink is applied. A static eliminator orprecharging device 4 controls the electrostatic charge on the freshlyprinted paper 2 which then enters chamber 5 where electrostatic guns 6discharge electrostatically charged powder. The powder covered paper 2then enters air knife 7 where powder which has not adhered to the ink isremoved. As the paper passes through heating tunnel 8, the resin meltsand fuses with the ink. Chill rolls 9 provide a drive for the paper 2and effect a cooling and leveling of the printed surface, which rendersthe printing cured.

The following examples are submitted to illustrate but not to limit thisinvention. The apparatus used to generate these examples is the same asthat described in the attached schematic drawing.

EXAMPLE I A non-drying process blue offset ink was used to print adetailed picture having some letter characters and a wide range ofhalf-tone density. The paper was electrostatically charged and a powderwas used having an average particle size of about 7 microns and havingthe following compositions:

Composition V1 M P.

Polyamide Resin 97.0 25UF Polyethylene Wax 2.5 2l5FPolytetrufluoroethylene (1.5 620F This powder was fed at a rate of 5grams/minute. The powder was then charged electrostatically with apolarity opposite to that of the paper. Excess powder was not removed.The printed and powdered paper was passed through an infrared heatingtunnel having a temperature of 550F. The surface emerged at atemperature of 350F. On cooling a cured glossy print was produced havinga thickness of about 5 microns.

EXAMPLE II The procedure of Example I was repeated except that the airknife was used to remove excess powder. A cured glossy image wasproduced having a thickness of about 5 microns.

EXAMPLE Ill The proceedure of Example ll was repeated except that therate at which powder was applied was reduced by one half. A cured,semi-gloss image was produced having a thickness of about 4 /2 microns.

EXAMPLE [V ing a solvent-free oil or liquid ink to a surface, the im'provement comprising:

a. applying a powder resin having an average particle size between about5-10 microns to the inked surface; and

b. curing the resinated ink to provide a non-raised printed surface witha thickness below about 7 microns.

2. The process of claim 1 comprising the additional step of providingsaid resin with about one-half to three percent powder by weight of apowdered wax.

3. The process of claim 1 in which said step of applying said resin tosaid surface is accomplished electrostatically.

4. The process of claim 1 in which said step of applying said resin tosaid surface is accomplished electrodynamically.

S. The process of claim 1 comprising the additional step of removingresin which does not adhere to the ink by blowing air across saidsurface.

6. A process of claim 1 in which said resin is thermoplastic and saidcuring step is accomplished by heating said surface to a temperature ofabout 50F. to F. above the melting point of said resin.

7. The process of claim 6 in which said step of heating is accomplishedby passing said surface through a heating tunnel.

8. The process of claim 6 in which said heating step is accomplished bydirect-flame heating.

9. The process of claim 6 in which said heating step is accomplished byinfrared heating.

10. The process of claim 1 comprising the additional step of leveling.

11. The process of claim 1 in which said resin is thermosetting and saidcuring step is accomplished by polymerization.

1. IN A PRINTING PROCESS COMPRISING THE STEP OF APPLYING A SOLVENT-FREEOIL OR LIQUID INK TO A SURFACE, THE IMPROVEMENT COMPRISING: A. APPLYINGA POWDER RESIN HAVING AN AVERAGE PARTICLE SIZE BETWEEN ABOUT 5-10MIVRONS TO THE INKED SURFACE, AND B. CURING THE RESINATED INK TO PROVIDEA NON-RAISED PRINTED SURFACE WITH A THICKNESS BELOW ABOUT 7 MICRONS. 2.The process of claim 1 comprising the additional step of providing saidresin with about one-half to three percent powder by weight of apowdered wax.
 3. The process of claim 1 in which said step of applyingsaid resin to said surface is accomplished electrostatically.
 4. Theprocess of claim 1 in which said step of applying said resin to saidsurface is accomplished electrodynamically.
 5. The process of claim 1comprising the additional step of removing resin which does not adhereto the ink by blowing air across said surface.
 6. A process of claim 1in which said resin is thermoplastic and said curing step isaccomplished by heating said surface to a temperature of about 50*F. to150*F. above the melting point of said resin.
 7. The process of claim 6in which said step of heating is accomplished by passing said surfacethrough a heating tunnel.
 8. The process of claim 6 in which saidheating step is accomplished by direct-flame heating.
 9. The process ofclaim 6 in which said heating step is accomplished by infrared heating.10. The process of claim 1 comprising the additional step of leveling.11. The process of claim 1 in which said resin is thermosetting and saidcuring step is accomplished by polymerization.